Electrical debonding type adhesive sheet, joined body, and joining and separation method for adherend

ABSTRACT

The present invention provides an electrical debonding type adhesive sheet capable of producing a joined body in which a voltage can be stably applied to an electrical debonding type adhesive layer. An electrical debonding type adhesive sheet according to a first embodiment of the present invention includes a first adhesive layer, a substrate for voltage application including an electroconductive layer and a base layer, and a second adhesive layer in this order, and has a first protrudent part, in which the first adhesive layer and the substrate for voltage application extend and protrude with respect to the second adhesive layer, and a second protrudent part, in which the substrate for voltage application extends from the first protrudent part and protrudes with respect to the first adhesive layer.

TECHNICAL FIELD

The present invention relates to electrical debonding type adhesivesheets, joined bodies including the adhesive sheets and adherends, andmethods for joining and separating adherends using the adhesive sheets.

There are growing demands regarding, for example, reworking forimproving yield in electronic-component production steps, etc. andrecycling for disassembling and recovering components after use. Inorder to meet such demands, a double-sided adhesive sheet having certainadhesive force and certain debonding properties is sometimes utilizedfor joining members in electronic-component manufacturing steps, etc.

Known as a double-sided adhesive sheet combining adhesive force anddebonding properties is an adhesive sheet (electrical debonding typeadhesive sheet) which includes an electrical debonding type adhesivelayer constituted of an electrically debondable adhesive composition andwhich undergoes debonding upon voltage application to the adhesive layer(Patent Document 1).

CITATION LIST Patent Literature

-   Patent Document 1: International Publication WO 2017/064925

SUMMARY OF THE INVENTION Technical Problems

Such an adhesive sheet may consist only of an electrical debonding typeadhesive layer, but is preferably an adhesive sheet including a baselayer, in view of handleability and suitability for distribution.

This base layer is required to have electrical conductivity for voltageapplication to the electrical debonding type adhesive layer. However, incases when a metal foil is used as the base, burrs are prone to resultwhen this adhesive sheet is punched. The presence of such burrs maycause a short circuit between the metal foil and an adherend, making itimpossible to apply a voltage to the electrical debonding type adhesivelayer.

It is hence preferable that a substrate for voltage application obtainedby forming an electroconductive layer, e.g., a vapor-deposited thinmetal film, on a base layer such as, for example, a PET film is used asa substrate in the electrical debonding type adhesive sheet.

Components which are joined to each other by such an electricaldebonding type adhesive sheet are debonded while applying a voltage tothe electrical debonding type adhesive layer, which is constituted of anelectrically debondable adhesive composition. By improving theefficiency of this voltage application, the efficiency of the wholeoperation of debonding can be improved.

Patent Document 1 discloses an electrical debonding type adhesive sheethaving a configuration including a protrudent part in which a substratefor voltage application extends with respect to a first adhesive layerand a second adhesive layer in a plane direction of the substrate forvoltage application and is exposed, in order to improve the efficiencyof voltage application. This configuration is intended to make anelectrical contact between a terminal of a voltage application deviceand the substrate for voltage application more apt to occur, by exposingsome of the substrate for voltage application, which is usually coveredwith an insulating adhesive layer.

However, such configuration is disadvantageous in that the protrudentpart is not fixed with an adhesive and is hence unstable and there is apossibility that the protrudent part might undesirably come intoelectrical contact with an unintended portion in applying a voltage,making it impossible to properly apply a voltage to the electricaldebonding type adhesive layer. Moreover, since the substrate for voltageapplication is thin and flexible, the contact with the terminal of avoltage application device is prone to be unstable and this is prone toresult in an increase in the number of steps for the operation ofdebonding.

There has hence been a desire for an electrical debonding type adhesivesheet capable of producing a joined body in which a voltage can be morestably applied to the electrical debonding type adhesive layer.

The present invention has been conceived under such circumstances, andan object of the present invention is to provide electrical debondingtype adhesive sheets capable of producing joined bodies in which avoltage can be stably applied to the electrical debonding type adhesivelayers. The present invention further provides joined bodies producedusing such electrical debonding type adhesive sheets and methods forjoining and separating adherends using such electrical debonding typeadhesive sheets.

Solution to the Problems

The present inventors diligently made investigations and, as a result,have discovered that those objects can be accomplished with electricaldebonding type adhesive sheets having specific configurations.

Specifically, an electrical debonding type adhesive sheet according to afirst embodiment of the present invention is an electrical debondingtype adhesive sheet including a substrate for voltage application, whichincludes an electroconductive layer and a base layer, a first adhesivelayer, which is constituted of an electrically debondable adhesive andis formed on the electroconductive layer of the substrate for voltageapplication, and a second adhesive layer, which is formed on the baselayer of the substrate for voltage application, the electrical debondingtype adhesive sheet having: a first protrudent part, in which the firstadhesive layer and the substrate for voltage application extend andprotrude with respect to the second adhesive layer in a plane directionof the electrical debonding type adhesive sheet; and a second protrudentpart, in which the substrate for voltage application extends from thefirst protrudent part and protrudes with respect to the first adhesivelayer in a plane direction of the electrical debonding type adhesivesheet.

A joined body according to the first embodiment of the present inventionis a joined body including the electrical debonding type adhesive sheetaccording to the first embodiment of the present invention, a firstadherend, and a second adherend, wherein the first protrudent part ofthe electrical debonding type adhesive sheet is folded back toward thesecond adhesive layer, the first adherend is adhered to the electricaldebonding type adhesive sheet by a portion of the first adhesive layerwhich is not folded back, and the second adherend is adhered to theelectrical debonding type adhesive sheet by both the second adhesivelayer and the folded portion of the first adhesive layer and is incontact with the electroconductive layer lying in the second protrudentpart.

A method for joining and separating adherends according to the firstembodiment of the present invention includes: folding back the firstprotrudent part of the electrical debonding type adhesive sheetaccording to the first embodiment of the present invention toward thesecond adhesive layer; adhering a first adherend to a portion of thefirst adhesive layer which is not folded back; adhering a secondadherend to both the second adhesive layer and the folded portion of thefirst adhesive layer, thereby joining the first adherend and the secondadherend to each other; and thereafter applying a voltage to the firstadhesive layer so as to result in a difference in potential in athickness direction thereof, thereby separating the first adherend andthe second adherend from each other.

An electrical debonding type adhesive sheet according to a secondembodiment of the present invention is an electrical debonding typeadhesive sheet including a substrate for voltage application, whichincludes an electroconductive layer and a base layer, a first adhesivelayer, which is constituted of an electrically debondable adhesive andis formed on the electroconductive layer of the substrate for voltageapplication, and a second adhesive layer, which is formed on the baselayer of the substrate for voltage application, the electrical debondingtype adhesive sheet having a protrudent part in which the secondadhesive layer and the substrate for voltage application extend andprotrude with respect to the first adhesive layer in a plane directionof the electrical debonding type adhesive sheet.

A joined body according to the second embodiment of the presentinvention is a joined body including the electrical debonding typeadhesive sheet according to the second embodiment of the presentinvention, a first adherend, and a second adherend, wherein the secondadherend is adhered to the electrical debonding type adhesive sheet bythe second adhesive layer, some of the electrical debonding typeadhesive sheet is folded back along an end of the second adherend sothat some of the second adherend is sandwiched, at least some of theprotrudent part is adhered, by the second adhesive layer, to thatsurface of the second adherend which is on the reverse side from thefirst adherend, and the first adherend is adhered to the electricaldebonding type adhesive sheet by a portion of the first adhesive layerwhich is not folded back.

A method for joining and separating adherends according to the secondembodiment of the present invention includes: folding back some of theelectrical debonding type adhesive sheet according to the secondembodiment of the present invention along an end of a second adherend sothat some of the second adherend is sandwiched, and adhering theelectrical debonding type adhesive sheet to the second adherend by thesecond adhesive layer; applying a portion of the first adhesive layerwhich is not folded back to a first adherend to join the first adherendand the second adherend to each other so that at least some of theprotrudent part is adhered, by the second adhesive layer, to thatsurface of the second adherend which is on the reverse side from thefirst adherend; and thereafter applying a voltage to the first adhesivelayer so as to result in a difference in potential in a thicknessdirection thereof, thereby separating the first adherend and the secondadherend from each other.

Advantageous Effects of Invention

The electrical debonding type adhesive sheets of the present inventioncan provide joined bodies that can be electrically debonded stably. Thejoined bodies of the present invention can be electrically debondedstably. The methods of the invention for joining and debonding adherendsrender stable electrical debonding possible.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagrammatic view of an electrical debonding type adhesivesheet according to the first embodiment of the present invention.

FIG. 2(a) is a slant view of one example of electrical debonding typeadhesive sheets according to the first embodiment of the presentinvention; and FIG. 2(b) is a slant view of another example ofelectrical debonding type adhesive sheets according to the firstembodiment of the present invention.

FIG. 3 is an exploded view of a joined body according to the firstembodiment of the present invention.

FIG. 4 is an enlarged view of the dotted-line-encircled portion of FIG.3.

FIG. 5 is an enlarged view of the dotted-line-encircled portion of FIG.2 in a modification example of the first embodiment of the presentinvention.

FIG. 6 is a diagrammatic view of a joined body according to the firstembodiment of the present invention which is being electricallydebonded.

FIG. 7 is a diagrammatic view of an electrical debonding type adhesivesheet according to the second embodiment of the present invention.

FIG. 8 is a diagrammatic view of a joined body according to the secondembodiment of the present invention.

FIG. 9 is an enlarged view of the dotted-line-encircled portion of FIG.8.

FIG. 10 is an enlarged view of the dotted-line-encircled portion of FIG.8 in a modification example of the second embodiment of the presentinvention.

FIG. 11 is a diagrammatic view of a joined body according to the secondembodiment of the present invention which is being electricallydebonded.

DESCRIPTION OF EMBODIMENTS

Modes for carrying out the present invention are explained in detailbelow. However, the present invention is not limited to the embodimentsdescribed below.

First Embodiment <Adhesive Sheet>

FIG. 1 is a diagrammatic view of an electrical debonding type adhesivesheet 10 according to the first embodiment of the present invention(hereinafter also referred to simply as “adhesive sheet 10 according tothis embodiment” or “adhesive sheet 10”). The adhesive sheet 10according to this embodiment is an electrical debonding type adhesivesheet including a substrate for voltage application 12, which includesan electroconductive layer 12 a and a base layer 12 b, a first adhesivelayer 11, which is constituted of an electrically debondable adhesiveand is formed on the electroconductive layer 12 a of the substrate forvoltage application 12, and a second adhesive layer 13, which is formedon the base layer 12 b of the substrate for voltage application 12, theelectrical debonding type adhesive sheet 10 having: a first protrudentpart 14, in which the first adhesive layer 11 and the substrate forvoltage application 12 extend and protrude with respect to the secondadhesive layer 13 in a plane direction of the electrical debonding typeadhesive sheet 10; and a second protrudent part 15, in which thesubstrate for voltage application 12 extends from the first protrudentpart and protrudes with respect to the first adhesive layer 11 in aplane direction of the electrical debonding type adhesive sheet 10.

(Constituent Elements of the Adhesive Sheet)

First, the layers and protrudent parts which constitute the adhesivesheet according to the first embodiment are explained.

The first adhesive layer 11 is an adhesive layer constituted of anelectrically debondable adhesive and includes both a polymer as anadhesive and an electrolyte.

Examples of the polymer included in the first adhesive layer 11 includeacrylic polymers, rubber-based polymers, vinyl-alkyl-ether-basedpolymers, silicone-based polymers, polyester-based polymers,polyamide-based polymers, urethane-based polymers, fluoropolymers, andepoxy-based polymers. The first adhesive layer 11 may include onepolymer as the only polymer or may include two or more polymers.

From the standpoints of inhibiting cost increase and attaining highproduction efficiency, it is preferable that the first adhesive layer 11includes an acrylic polymer. An acrylic polymer is a polymer whichincludes monomer units derived from an alkyl acrylate and/or an alkylmethacrylate, as main monomer units contained in a largest amount interms of mass proportion. Hereinafter, “(meth)acrylic” represents“acrylic” and/or “methacrylic”.

In the case where the first adhesive layer 11 includes an acrylicpolymer, it is preferable that the acrylic polymer includes monomerunits derived from an alkyl (meth)acrylate in which the alkyl group has1-14 carbon atoms. Examples of the alkyl (meth)acrylate include methyl(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl(meth)acrylate, n-butyl (meth)acrylate, sec-butyl (meth)acrylate,1,3-dimethylbutyl acrylate, pentyl (meth)acrylate, isopentyl(meth)acrylate, hexyl (meth)acrylate, 2-ethylbutyl (meth)acrylate,heptyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate,2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl(meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate,n-dodecyl (meth)acrylate, n-tridecyl (meth)acrylate, and n-tetradecyl(meth)acrylate. Preferred of these are n-butyl (meth)acrylate, sec-butyl(meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate,2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, and isononyl(meth)acrylate. One alkyl (meth)acrylate may be used, or two or morealkyl (meth)acrylates may be used.

In the acrylic polymer, the proportion of the monomer units derived froman alkyl (meth)acrylate in which the alkyl group has 1-14 carbon atomsis preferably 50% by mass or higher, more preferably 60% by mass orhigher, still more preferably 70% by mass or higher, yet still morepreferably 80% by mass or higher, from the standpoint of enabling thefirst adhesive layer 11 to have high adhesive force. That is, theproportion of the alkyl (meth)acrylate in which the alkyl group has 1-14carbon atoms to the sum of the starting-material monomers for formingthe acrylic polymer is preferably 50% by mass or higher, more preferably60% by mass or higher, still more preferably 70% by mass or higher, yetstill more preferably 80% by mass or higher, from the standpoint ofenabling the first adhesive layer 11 to have high adhesive force.

In the case where the first adhesive layer 11 includes an acrylicpolymer, it is preferable that the acrylic polymer contains monomerunits derived from a monomer containing a polar group, from thestandpoint of enabling the first adhesive layer 11 to have high adhesiveforce. Examples of the monomer containing a polar group includecarboxyl-group-containing monomers, hydroxyl-group-containing monomers,and vinyl-group-containing monomers.

Examples of the carboxyl-group-containing monomers include acrylic acid,methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonicacid, isocrotonic acid, carboxyethyl (meth)acrylate, and carboxypentyl(meth)acrylate. Preferred of these are acrylic acid and methacrylicacid. One carboxyl-group-containing monomer may be used, or two or morecarboxyl-group-containing monomers may be used.

Examples of the hydroxyl-group-containing monomers include2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate,4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate,8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate,12-hydroxylauryl (meth)acrylate, (4-hydroxymethylcyclohexyl)methylacrylate, N-methylol(meth)acrylamide, vinyl alcohol, allyl alcohol,2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, and diethyleneglycol monovinyl ether. Preferred of these is 2-hydroxyethyl(meth)acrylate. One hydroxyl-group-containing monomer may be used, ortwo or more hydroxyl-group-containing monomers may be used.

Examples of the vinyl-group-containing monomers include vinyl acetate,vinyl propionate, and vinyl laurate. Preferred of these is vinylacetate. One vinyl-group-containing monomer may be used, or two or morevinyl-group-containing monomers may be used.

In the acrylic polymer, the proportion of the monomer units derived froma monomer containing a polar group is preferably 0.1% by mass or higherfrom the standpoint of enabling the first adhesive layer 11 to retaincohesive force and thereby preventing the first adhesive layer 11 fromcausing an adhesive transfer to the debonded adherend surface. That is,the proportion of the monomer containing a polar group to the sum of thestarting-material monomers for constituting the acrylic polymer ispreferably 0.1% by mass or higher from the standpoints of ensuringcohesive force and preventing the occurrence of an adhesive transfer.Meanwhile, from the standpoint of causing the acrylic polymer toproperly exhibit properties attributable to the monomer units derivedfrom the alkyl (meth)acrylate, in which the alkyl group has 1-14 carbonatoms, the proportion of the monomer units derived from a monomercontaining a polar group in the acrylic polymer is preferably 30% bymass or less. That is, the proportion of the monomer containing a polargroup to the sum of the starting-material monomers for constituting theacrylic polymer is preferably 30% by mass or less from the standpoint ofcausing the acrylic polymer to exhibit the properties.

Methods for polymerizing such monomers to obtain the acrylic polymer arenot particularly limited, and known methods can be used. Examples ofpolymerization techniques include solution polymerization, emulsionpolymerization, bulk polymerization, and suspension polymerization.

The content of the polymer in the first adhesive layer 11 is preferably70% by mass or higher, more preferably 80% by mass or higher, still morepreferably 85% by mass or higher, yet still more preferably 90% by massor higher, from the standpoint of enabling the first adhesive layer 11to have sufficient adhesive force.

The electrolyte contained in the first adhesive layer 11 is a substancecapable of being ionized into one or more anions and one or morecations. Examples of the electrolyte include ionic liquids, alkali metalsalts, and alkaline-earth metal salts. The electrolyte contained in thefirst adhesive layer 11 is preferably an ionic liquid from thestandpoint of enabling the first adhesive layer 11 to have satisfactoryelectrically debonding properties. The ionic liquid is a salt which isliquid at room temperature (about 25° C.), and includes an anion and acation.

In the case where the first adhesive layer 11 contains an ionic liquid,it is preferable that this ionic liquid includes one or more anionswhich are at least one anion selected from the group consisting of(FSO₂)₂N⁻, (CF₃SO₂)₂N⁻, (CF₃CF₂SO₂)₂N⁻, (CF₃SO₂)₃C⁻, Br⁻, AlCl₄ ⁻,Al₂Cl₇ ⁻, NO₃ ⁻, BF₄ ⁻, PF₆ ⁻, CH₃COO⁻, CF₃COO⁻, CF₃CF₂CF₂COO⁻, CF₃SO₃⁻, CF₃(CF₂)₃SO₃ ⁻, AsF₆ ⁻, SbF₆ ⁻, and F(HF)_(n) ⁻. Preferred of theseanions are (FSO₂)₂N⁻ [bis(fluorosulfonyl)imide anion] and (CF₃SO₂)₂N⁻[bis(trifluoromethanesulfonyl)imide anion], because these anions arechemically stable and are suitable for attaining the electricallydebonding properties of the first adhesive layer 11.

In the case where the first adhesive layer 11 contains an ionic liquid,it is preferable that this ionic liquid includes one or more cationswhich are at least one cation selected from the group consisting ofimidazolium cations, pyridinium cations, pyrrolidinium cations, andammonium cations.

Examples of the imidazolium cations include 1-methylimidazolium cation,1-ethyl-3-methylimidazolium cation, 1-propyl-3-methylimidazolium cation,1-butyl-3-methylimidazolium cation, 1-pentyl-3-methylimidazolium cation,1-hexyl-3-methylimidazolium cation, 1-heptyl-3-methylimidazolium cation,1-octyl-3-methylimidazolium cation, 1-nonyl-3-methylimidazolium cation,1-undecyl-3-methylimidazolium cation, 1-dodecyl-3-methylimidazoliumcation, 1-tridecyl-3-methylimidazolium cation,1-tetradecyl-3-methylimidazolium cation,1-pentadecyl-3-methylimidazolium cation, 1-hexadecyl-3-methylimidazoliumcation, 1-heptadecyl-3-methylimidazolium cation,1-octadecyl-3-methylimidazolium cation, 1-undecyl-3-methylimidazoliumcation, 1-benzyl-3-methylimidazolium cation,1-butyl-2,3-dimethylimidazolium cation, and 1,3-bis(dodecyl)imidazoliumcation.

Examples of the pyridinium cations include 1-butylpyridinium cation,1-hexylpyridinium cation, 1-butyl-3-methylpyridinium cation,1-butyl-4-methylpyridinium cation, and 1-octyl-4-methylpyridiniumcation.

Examples of the pyrrolidinium cations include1-ethyl-1-methylpyrrolidinium cation and 1-butyl-1-methylpyrrolidiniumcation.

Examples of the ammonium cations include tetraethylammonium cation,tetrabutylammonium cation, methyltrioctylammonium cation,tetradecytrihexylammonium cation, glycidyltrimethylammonium cation, andtrimethylaminoethyl acrylate cation.

Especially preferred as the ionic liquid in the first adhesive layer 11is an ionic liquid including both (FSO₂)₂N⁻ [bis(fluorosulfonyl)imideanion] and a cation having a molecular weight of 160 or less, from thestandpoint of utilizing the high diffusibility of the cations to imparthigh electrically debonding properties to the first adhesive layer 11.Examples of the cation having a molecular weight of 160 or less include1-methylimidazolium cation, 1-ethyl-3-methylimidazolium cation,1-propyl-3-methylimidazolium cation, 1-butyl-3-methylimidazolium cation,1-pentyl-3-methylimidazolium cation, 1-butylpyridinium cation,1-hexylpyridinium cation, 1-butyl-3-methylpyridinium cation,1-butyl-4-methylpyridinium cation, 1-ethyl-1-methylpyrrolidinium cation,1-butyl-1-methylpyrrolidinium cation, tetraethylammonium cation,glycidyltrimethylammonium cation, and trimethylaminoethyl acrylatecation.

Examples of commercial products of ionic liquids which can be containedin the first adhesive layer 11 include “ELEXCEL AS-110”, “ELEXCELMP-442”, “ELEXCEL IL-210”, “ELEXCEL MP-471”, “ELEXCEL MP-456”, and“ELEXCEL AS-804”, all manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.

Examples of the alkali metal salts include LiCl, Li₂SO₄, LiBF₄, LiPF₆,LiClO₄, LiAsF₆, LiCF₃SO₃, LiN(SO₂CF₃)₂, LiN(SO₂C₂F₅)₂, LiC(SO₂CF₃)₃,NaCl, Na₂SO₄, NaBF₄, NaPF₆, NaClO₄, NaAsF₆, NaCF₃SO₃, NaN(SO₂CF₃)₂,NaN(SO₂C₂F₅)₂, NaC(SO₂CF₃)₃, KCl, K₂SO₄, KBF₄, KPF₆, KC₁₀₄, KAsF₆,KCF₃SO₃, KN(SO₂CF₃)₂, KN(SO₂C₂F₅)₂, and KC(SO₂CF₃)₃.

The content of an ionic liquid in the first adhesive layer 11 per 100parts by mass of the polymer in the first adhesive layer 11 is, forexample, 0.1 part by mass or higher from the standpoint of impartingelectrically debonding properties to the first adhesive layer 11. Fromthe standpoint of attaining better electrically debonding properties,the content of the ionic liquid is preferably 0.5 parts by mass orhigher, more preferably 0.6 parts by mass or higher, still morepreferably 0.8 parts by mass or higher, especially preferably 1.0 partby mass or higher, most preferably 1.5 parts by mass or higher. From thestandpoint of enabling the first adhesive layer 11 to attain asatisfactory balance between satisfactory adhesive force andelectrically debonding properties, the content of the ionic liquid inthe first adhesive layer 11, per 100 parts by mass of the polymer in thefirst adhesive layer 11, is preferably 30 parts by mass or less, morepreferably 20 parts by mass or less, still more preferably 15 parts bymass or less, especially preferably 10 parts by mass or less, mostpreferably 5 parts by mass or less.

The first adhesive layer 11 may contain other ingredients so long as theinclusion thereof does not lessen the effects of the present invention.Examples of the ingredients include tackifiers, silane coupling agents,colorants, pigments, dyes, surface lubricants, leveling agents,softeners, antioxidants, aging inhibitors, light stabilizers,polymerization inhibitors, inorganic or organic fillers, metal powders,particulate substances, and flaky substances. The content of suchingredients may be determined in accordance with intended uses so longas the effects of the present invention are not lessened. For example,the content thereof is 10 parts by mass or less per 100 parts by mass ofthe polymer.

The thickness of the first adhesive layer 11 is not particularlylimited. However, from the standpoint of enabling the first adhesivelayer 11 to have satisfactory adhesiveness, the thickness thereof ispreferably 1 μm or larger, more preferably 3 μm or larger, still morepreferably 5 μm or larger, especially preferably 8 μm or larger.Meanwhile, from the standpoint of attaining a reduction in the voltageto be applied in adherend debonding, the thickness of the first adhesivelayer 11 is preferably 1,000 μm or less, more preferably 500 μm or less,still more preferably 100 μm or less, especially preferably 30 μm orless.

The second adhesive layer 13 includes a polymer for causing the secondadhesive layer 13 to exhibit adhesiveness. Ingredients which can beincluded in the second adhesive layer 13 and the contents thereof,except for electrolytes, are the same as the ingredients which can beincluded in the first adhesive layer 11 and the contents thereof, whichwere described above.

The thickness of the second adhesive layer 13 is not particularlylimited. However, from the standpoint of enabling the second adhesivelayer 13 to have satisfactory adhesiveness, the thickness thereof ispreferably 1 μm or larger, more preferably 3 μm or larger, still morepreferably 5 μm or larger, especially preferably 8 μm or larger.Meanwhile, the thickness of the second adhesive layer 13 is preferably1,000 μm or less, more preferably 500 μm or less, still more preferably100 μm or less.

The substrate for voltage application 12 is not particularly limited solong as it has a multilayer structure including an electroconductivelayer 12 a and a base layer 12 b. For example, use can be made of analuminum-coated film including a plastic film and a vapor-depositedaluminum film formed thereon.

The thickness of the substrate for voltage application 12 is notparticularly limited. However, the thickness thereof is preferably 10 μmor larger, more preferably 12 μm or larger, still more preferably 25 μmor larger. Meanwhile, the thickness of the substrate for voltageapplication 12 is preferably 1,000 μm or less, more preferably 500 μm orless, still more preferably 300 μm or less, especially preferably 100 μmor less.

The base layer 12 b is a portion functioning as a support. Examplesthereof include plastic bases, fibrous bases, paper bases, and laminatesof these. The base layer 12 b may have a single-layer structure or maybe composed of two or more layers. The base layer 12 b may haveundergone any of various treatments including a back-surface treatment,antistatic treatment, and priming, according to need.

The thickness of the base layer 12 b is not particularly limited.However, the thickness thereof is preferably 10 μm or larger, morepreferably 12 μm or larger, still more preferably 25 μm or larger.Meanwhile, the thickness of the base layer 12 b is preferably 1,000 μmor less, more preferably 500 μm or less, still more preferably 300 μm orless, especially preferably 100 μm or less.

The electroconductive layer 12 a is a layer having electricalconductivity and is constituted of, for example, a metal or anelectroconductive polymer. Such electroconductive layer 12 a can beformed by plating, chemical vapor deposition, sputtering, etc.

The thickness of the electroconductive layer 12 a is not particularlylimited. However, the thickness thereof is preferably 0.001 μm orlarger, more preferably 0.01 μm or larger, still more preferably 0.03 μmor larger, especially preferably 0.05 μm or larger. Meanwhile, thethickness thereof is preferably 1,000 μm or less, more preferably 500 μmor less, still more preferably 300 μm or less, especially preferably 50μm or less, most preferably 10 μm or less.

The first protrudent part 14 is a portion where the first adhesive layer11 and the substrate for voltage application 12 extend and protrude withrespect to the second adhesive layer 13 in a plane direction of theelectrical debonding type adhesive sheet 10. The second protrudent part15 is a portion where the substrate for voltage application 12 extendsfrom the first protrudent part 14 and protrudes with respect to thefirst adhesive layer 11 in a plane direction of the electrical debondingtype adhesive sheet 10.

The first protrudent part 14 and the second protrudent part 15 are notparticularly limited in the dimensions and shapes thereof. For example,the adhesive sheet 10 may be a tape-shaped adhesive sheet 10 having aconfiguration that includes a first protrudent part 14 and a secondprotrudent part 15 which are disposed in an end portion of the adhesivesheet 10, as shown in FIG. 2(a), or may be a sheet-shaped adhesive sheet10 having a configuration that includes a first protrudent part 14 and asecond protrudent part 15 which project, as shown in FIG. 2(b).

Separators (release liners) may have be disposed on the surfaces of thefirst adhesive layer 11 and second adhesive layer 13 of the adhesivesheet 10 according to the first embodiment. The separators are anelement for protecting the first adhesive layer 11 and second adhesivelayer 13 of the adhesive sheet 10 from exposure, and are peeled from theadhesive sheet 10 when the adhesive sheet 10 is applied to adherends.The adhesive sheet 10 may be in a form in which the adhesive sheet 10 isin the state of having been sandwiched between two separators, or may bein a form obtained by winding the adhesive sheet 10 and a separator intoa roll so that layers of the adhesive sheet 10 alternate with layers ofthe separator. Examples of the separator include bases having areleasing layer, lowly bondable bases constituted of a fluoropolymer,and lowly bondable bases constituted of a nonpolar polymer. The surfaceof the separator may have undergone a release treatment, antifoulingtreatment, or antistatic treatment. The thickness of the separator is,for example, 5-200 μm.

(Adhesive Force of the Adhesive Sheet)

It is preferable that the adhesive surfaces of the adhesive sheet 10,that is, the surface on the first adhesive layer 11 side and the surfaceon the second adhesive layer 13 side, have a 180° peel adhesive force(application to SUS304 plate; pulling speed, 300 mm/min; peelingtemperature, 23° C.) of 0.1 N/10 mm or higher, from the standpoint ofattaining satisfactory adhesive force. The 180° peel adhesive force ofthe adhesive sheet 10 can be measured, for example, in the followingmanner in accordance with JIS Z 0237.

The adhesive sheet 10 which is covered on both sides with separators isexamined in the following manner. First, one of the separators is peeledoff, and a poly(ethylene terephthalate) (PET) film having a thickness of50 μm is thereafter adhered to the exposed adhesive surface to line theadhesive sheet 10. Next, a test piece [10 mm (width)×100 mm (length)] iscut out of the lined adhesive sheet 10. Subsequently, the otherseparator is peeled from this test piece and the test piece is thenapplied to a stainless-steel plate (SUS304) as an adherend. Thereafter,the test piece is press-bonded to the adherend by rolling a 2-kg rollerthereon forward and backward once. This specimen is allowed to standstill for 30 minutes and then examined for 180° peel adhesive force(pulling speed, 300 mm/min; peel temperature, 23° C.) using a peeltester (trade name “Variable-Angle Peel Tester YSP”, manufactured byAsahi Seiko Co., Ltd.).

(Methods for producing the Adhesive Sheet)

The adhesive sheet 10 is produced, for example, in the following manner.First, an adhesive composition (first composition) for forming a firstadhesive layer 11 and an adhesive composition (second composition) forforming a second adhesive layer 13 are produced. Next, the firstcomposition is applied to the surface of the electroconductive layer 12a of a substrate for voltage application 12 and dried, thereby forming afirst adhesive layer 11. Next, the second composition is applied to thesurface of the base layer 12 b of the substrate for voltage application12 and dried, thereby forming a second adhesive layer 13. The adhesivesheet 10 can be produced, for example, in this manner.

Alternatively, the adhesive sheet 10 may be produced by the so-calledtransfer method. Specifically, a first adhesive layer 11 and a secondadhesive layer 13 are first formed on respective separators (releaseliners). The first adhesive layer 11 is formed by applying the firstcomposition, which is for forming a first adhesive layer 11, to thereleasing surface of a given separator to form a coating film and thendrying the coating film. The second adhesive layer 13 is formed byapplying the second composition, which is for forming a second adhesivelayer 13, to the releasing surface of a given separator to form acoating film and then drying the coating film. Next, the first adhesivelayer 11 having the separator adherent thereto is adhered to the surfaceof the electroconductive layer 12 a of a substrate for voltageapplication 12. Subsequently, the second adhesive layer 13 having theseparator adherent thereto is adhered to the surface of the base layer12 b of the substrate for voltage application 12. The adhesive sheet 10can be produced, for example, in this manner.

<Joined Body and Method for Joining and Separating Adherends>

Next, an explanation is given on a joined body obtained using theadhesive sheet 10 according to the first embodiment and a method forjoining and separating adherends using the adhesive sheet 10 accordingto the first embodiment.

FIG. 3 is an exploded view of a joined body 40 according to the firstembodiment of the present invention (hereinafter also referred to simplyas “joined body 40 according to this embodiment” or “joined body 40”).FIG. 4 is an enlarged view of the dotted-line-encircled portion of FIG.3.

The joined body 40 according to this embodiment is a joined bodyincluding the adhesive sheet 10 according to this embodiment, a firstadherend 20, and a second adherend 30, wherein the first protrudent part14 of the adhesive sheet 10 is folded back toward the second adhesivelayer 13, the first adherend 20 is adhered to the electrical debondingtype adhesive sheet 10 by a portion of the first adhesive layer 11 whichis not folded back, and the second adherend 30 is adhered to theelectrical debonding type adhesive sheet 10 by both the second adhesivelayer 13 and the folded portion of the first adhesive layer 11 and is incontact with the electroconductive layer lying in the second protrudentpart 15.

The method for joining and separating adherends according to thisembodiment includes: folding back the first protrudent part 14 of theadhesive sheet 10 according to this embodiment toward the secondadhesive layer 13; adhering a first adherend to a portion of the firstadhesive layer 11 which is not folded back; adhering a second adherend30 to both the second adhesive layer 13 and the folded portion of thefirst adhesive layer 11, thereby joining the first adherend 20 and thesecond adherend 30 to each other; and thereafter applying a voltage tothe first adhesive layer 11 so as to result in a difference in potentialin a thickness direction thereof, thereby separating the first adherend20 and the second adherend 30 from each other.

Specifically, when the adhesive sheet 10 is used in joining a firstadherend 20 and a second adherend 30, the first protrudent part 14 isfolded back toward the second adhesive layer 13 as shown in FIG. 4. Thatportion of the first adhesive layer 11 which is not folded back (thatis, the upper surface in FIG. 4) is applied to the first adherend 20,while the second adhesive layer and that portion of the first adhesivelayer 11 which lies in the folded first protrudent part 14 are appliedto the second adherend 30. In this operation, the position at which thefirst protrudent part 14 is folded is not particularly limited. Thefirst protrudent part 14 may be folded back along the end of the secondadhesive layer 13 as shown in FIG. 4, or may be folded back at aposition other than the end of the second adhesive layer 13 as shown inFIG. 5.

By thus joining the first adherend 20 and the second adherend 30 to eachother, the second adherend 30 is made to be in stable electrical contactwith the electroconductive layer 12 a of the adhesive sheet 10 in regionB shown in FIG. 4 (or region B′ shown in FIG. 5). Furthermore, since thesecond adherend 30 is adhered to the adhesive sheet 10 by both thesecond adhesive layer 13 and that portion of the first adhesive layer 11which lies in the folded first protrudent part 14, in regions A and Cshown in FIG. 4 (or regions A′ and C′ shown in FIG. 5), stable adhesioncan be ensured. There is hence no possibility that the electroconductivelayer 12 a of the substrate for voltage application 12 might come intocontact with an unintended portion to make it impossible to properlyapply a voltage to the first adhesive layer 11.

Furthermore, since the first protrudent part 14 is configured of some ofthe first adhesive layer 11 and some of the substrate for voltageapplication 12, that is, since the second adhesive layer 13 does not liein the first protrudent part 14, the increase in thickness due to thefolding is minimum. It is hence possible to attain stable joining and toensure a stable electrical connection between the second adherend 30 andthe electroconductive layer 12 a.

The first adherend 20 and the second adherend 30 have electricalconductivity. Examples of materials constituting such adherends includealuminum, copper, iron, silver, and alloys containing these. Thematerials may be electroconductive polymers, etc. Electricalconductivity is required of at least portions necessary for producingthe effects of the present invention. It is only required in the firstadherend 20 that at least the portion which is in contact with the firstadhesive layer 11 and a portion with which a terminal of a voltageapplication device is to be contacted have electrical conductivity andthese portions are electrically connected. In the second adherend, it isonly required that at least the portion which is in contact with theelectroconductive layer 12 a of the substrate for voltage application 12and a portion with which the other terminal of the voltage applicationdevice is to be contacted have electrical conductivity and theseportions are electrically connected.

In FIG. 6 is shown a diagrammatic view of the joined body 40 accordingto this embodiment in which the first adherend 20 and the secondadherend 30 are being debonded. The first adherend 20 and the secondadherend 30 are debonded while applying a voltage to the first adhesivelayer 11 via the first adherend 20 and the electroconductive layer 12 aof the adhesive sheet 10.

In the joined body 40 according to this embodiment, theelectroconductive layer 12 a of the adhesive sheet 10 is in electricalcontact with the second adherend 30 and, hence, a voltage can be stablyapplied by contacting the terminals of a voltage application device withthe first adherend 20 and the second adherend 30.

From the standpoint of operation efficiency, it is especially preferablein the voltage application that the terminals of a voltage applicationdevice are contacted, from the same direction, with the first adherend20 and the second adherend 30 as shown in FIG. 6.

The voltage to be applied to the first adhesive layer 11 is preferably 1V or higher, more preferably 3 V or higher, still more preferably 6 V orhigher. Meanwhile, the applied voltage is preferably 100 V or less, morepreferably 50 V or less, still more preferably 30 V or less, especiallypreferably 15 V or less. Applied voltages within such a range aresuitable because the operation of separating the joined body can beefficiently performed. For example, in cases when the applied voltage iswithin such a range, an easily available power source such as a drybattery can be used for the voltage application device.

It is preferable that the period of voltage application to the firstadhesive layer 11 is short. Specifically, the period of voltageapplication is preferably 60 seconds or less, more preferably 40 secondsor less, still more preferably 20 seconds or less. Voltage applicationperiods within such a range are suitable for heightening the efficiencyof the operation of separating the joined body.

Those preferred ranges of applied voltage and application period applyalso in the second embodiment described below.

Second Embodiment <Adhesive Sheet>

FIG. 7 is a diagrammatic view of an electrical debonding type adhesivesheet 110 according to the second embodiment of the present invention(hereinafter also referred to simply as “adhesive sheet according tothis embodiment” or “adhesive sheet 110”). The adhesive sheet 110according to this embodiment is an electrical debonding type adhesivesheet 110 including a substrate for voltage application 112, whichincludes an electroconductive layer 112 a and a base layer 112 b, afirst adhesive layer 111, which is constituted of an electricallydebondable adhesive and is formed on the electroconductive layer 112 aof the substrate for voltage application 112, and a second adhesivelayer 113, which is formed on the base layer 112 b of the substrate forvoltage application 112, the electrical debonding type adhesive sheet110 having a protrudent part 114 in which the second adhesive layer 113and the substrate for voltage application 112 extend and protrude withrespect to the first adhesive layer 111 in a plane direction of theelectrical debonding type adhesive sheet 110.

The layers constituting the adhesive sheet according to the secondembodiment are the same as in the adhesive sheet according to the firstembodiment, and the only difference is the configuration of theprotrudent part. The following explanation is given only on points inwhich the adhesive sheet according to this embodiment differs from theadhesive sheet according to the first embodiment.

The protrudent part 114 in the adhesive sheet 110 according to thesecond embodiment is a portion where the first adhesive layer 111 andthe substrate for voltage application 112 extend and protrude withrespect to the second adhesive layer 113 in a plane direction of theelectrical debonding type adhesive sheet 110. The protrudent part 114 isnot particularly limited in the dimensions and shape thereof. Forexample, the adhesive sheet 110 may be a tape-shaped adhesive sheethaving a configuration that includes a protrudent part 114 disposed inan end portion of the adhesive sheet or may be a sheet-shaped adhesivesheet having a configuration that includes a protrudent part 114 whichprojects, as explained above with regard to the first protrudent part 14and second protrudent part 15 of the first embodiment.

<Joined Body and Method for Joining and Separating Adherends>

Next, an explanation is given on a joined body obtained using theadhesive sheet 110 according to the second embodiment and a method forjoining and separating adherends using the adhesive sheet 110 accordingto the second embodiment.

FIG. 8 is an exploded view of a joined body 140 according to the secondembodiment of the present invention (hereinafter also referred to simplyas “joined body 140 according to this embodiment” or “joined body 140”).FIG. 9 is an enlarged view of the dotted-line-encircled portion of FIG.8.

The joined body 140 according to this embodiment is a joined bodyincluding the adhesive sheet 110 according to this embodiment, a firstadherend 120, and a second adherend 130, wherein the second adherend 130is adhered to the electrical debonding type adhesive sheet by the secondadhesive layer 130, some of the adhesive sheet 110 is folded back alongan end of the second adherend 130 so that some of the second adherend130 is sandwiched, at least some of the protrudent part 114 is adhered,by the second adhesive layer 113, to that surface of the second adherend130 which is on the reverse side from the first adherend 120, and thefirst adherend 120 is adhered to the adhesive sheet 110 by a portion ofthe first adhesive layer 111 which is not folded back.

The method for joining and separating adherends according to thisembodiment includes: folding back some of the adhesive sheet 110according to this embodiment along an end of a second adherend 130 sothat some of the second adherend 130 is sandwiched, and adhering theadhesive sheet 110 to the second adherend 130 by the second adhesivelayer 113; applying a portion of the first adhesive layer 111 which isnot folded back to a first adherend 120 to join the first adherend 120and the second adherend 130 to each other so that at least some of theprotrudent part 114 is adhered, by the second adhesive layer 113, tothat surface of the second adherend 130 which is on the reverse sidefrom the first adherend 120; and thereafter applying a voltage to thefirst adhesive layer 111 so as to result in a difference in potential ina thickness direction thereof, thereby separating the first adherend 120and the second adherend 130 from each other.

Specifically, when the adhesive sheet 110 is used in joining a firstadherend 120 and a second adherend 130, some of the adhesive sheet 110is folded back along an end of the second adherend 130 so that some ofthe second adherend 130 is sandwiched, as shown in FIG. 9. As a result,at least some of the protrudent part 114 is adhered, by the secondadhesive layer 113, to that surface of the second adherend 130 which ison the reverse side from the first adherend 120. In this operation, theposition at which the adhesive sheet 110 is folded is not particularlylimited. Some of the adhesive sheet 110 may be folded back along the endof the first adhesive layer 111 as shown in FIG. 9, or may be foldedback at a portion other than the protrudent part 114 as shown in FIG.10. It is, however, preferable that some of the adhesive sheet 110 isfolded back along the end of the first adhesive layer 111.

The first adherend 120 has electrical conductivity like the firstadherend 20 in the first embodiment. Meanwhile, the second adherend 130in this embodiment may or may not have electrical conductivity.

In the joined body 140 in which the first adherend 120 and the secondadherend 130 are thus joined to each other, the exposed portion of thesubstrate for voltage application 112 which lies in the protrudent partis adhered, by the second adhesive layer 113, to that surface of thesecond adherend 130 which is on the reverse side from the firstadherend. Since that portion of the substrate for voltage application112 is hence stable, there is no possibility that the electroconductivelayer 112 a of the substrate for voltage application 112 might come intocontact with an unintended portion to make it impossible to properlyapply a voltage to the first adhesive layer 111.

In FIG. 11 is shown a diagrammatic view of the joined body 140 accordingto this embodiment in which the first adherend 120 and the secondadherend 130 are being debonded. The first adherend 120 and the secondadherend 130 are debonded while applying a voltage to the first adhesivelayer 111 via the first adherend 120 and the electroconductive layer 112a of the adhesive sheet 110.

FIG. 11 shows a diagrammatic view of the joined body 140 according tothis embodiment which is being electrically debonded. In this joinedbody 140, it is possible to apply a voltage to the first adhesive layer111 of the adhesive sheet 110 via the first adherend 120 and thatportion of the electroconductive layer 112 a which lies in theprotrudent part that is folded back so that some of the second adherend130 is sandwiched. Stable voltage application is hence possible.

From the standpoint of operation efficiency, it is especially preferablein the voltage application that the terminals of a voltage applicationdevice are contacted from the same direction, as shown in FIG. 11.

In the joined body 40 according to this embodiment, some of the adhesivesheet 110 is folded back along an end of the second adherend 130 so thatsome of the second adherend 130 is sandwiched, and at least some of theprotrudent part is adhered to that surface of the second adherend 130which is on the reverse side from the first adherend 120. It is hencepossible to stably perform voltage application by contacting theterminals of a voltage application device with that portion of theelectroconductive layer 112 a which is exposed in the protrudent partand with the first adherend 120.

From the standpoint of operation efficiency, it is especially preferablein the voltage application that the terminals of a voltage applicationdevice are contacted, from the same direction, with the first adherend120 and the second adherend 130, as shown in FIG. 11.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof. This application is basedon a Japanese patent application filed on Mar. 8, 2018 (Application No.2018-42353), the entire contents thereof being incorporated herein byreference. All the references cited here are incorporated herein as awhole.

REFERENCE SIGNS LIST

-   10, 110: Electrical debonding type adhesive sheet-   11, 111: First adhesive layer-   12, 112: Substrate for voltage application    -   12 a, 112 a: Electroconductive layer    -   12 b, 112 b: Base layer-   13, 113: Second adhesive layer-   14: First protrudent part-   15: Second protrudent part-   20, 120: First adherend-   30, 130: Second adherend-   40, 140: Joined body-   50, 60, 150, 160: Terminal-   114: Protrudent part

1. An electrical debonding type adhesive sheet comprising a substratefor voltage application, which comprises an electroconductive layer anda base layer, a first adhesive layer, which is constituted of anelectrically debondable adhesive and is formed on the electroconductivelayer of the substrate for voltage application, and a second adhesivelayer, which is formed on the base layer of the substrate for voltageapplication, the electrical debonding type adhesive sheet having: afirst protrudent part, in which the first adhesive layer and thesubstrate for voltage application extend and protrude with respect tothe second adhesive layer in a plane direction of the electricaldebonding type adhesive sheet; and a second protrudent part, in whichthe substrate for voltage application extends from the first protrudentpart and protrudes with respect to the first adhesive layer in a planedirection of the electrical debonding type adhesive sheet.
 2. A joinedbody comprising the electrical debonding type adhesive sheet accordingto claim 1, a first adherend, and a second adherend, wherein the firstprotrudent part of the electrical debonding type adhesive sheet isfolded back toward the second adhesive layer, the first adherend isadhered to the electrical debonding type adhesive sheet by a portion ofthe first adhesive layer which is not folded back, and the secondadherend is adhered to the electrical debonding type adhesive sheet byboth the second adhesive layer and the folded portion of the firstadhesive layer and is in contact with the electroconductive layer lyingin the second protrudent part.
 3. A method for joining and separatingadherends, the method comprising: folding back the first protrudent partof the electrical debonding type adhesive sheet according to claim 1toward the second adhesive layer; adhering a first adherend to a portionof the first adhesive layer which is not folded back; adhering a secondadherend to both the second adhesive layer and the folded portion of thefirst adhesive layer, thereby joining the first adherend and the secondadherend to each other; and thereafter applying a voltage to the firstadhesive layer so as to result in a difference in potential in athickness direction thereof, thereby separating the first adherend andthe second adherend from each other.
 4. An electrical debonding typeadhesive sheet comprising a substrate for voltage application, whichcomprises an electroconductive layer and a base layer, a first adhesivelayer, which is constituted of an electrically debondable adhesive andis formed on the electroconductive layer of the substrate for voltageapplication, and a second adhesive layer, which is formed on the baselayer of the substrate for voltage application, the electrical debondingtype adhesive sheet having a protrudent part in which the secondadhesive layer and the substrate for voltage application extend andprotrude with respect to the first adhesive layer in a plane directionof the electrical debonding type adhesive sheet.
 5. A joined bodycomprising the electrical debonding type adhesive sheet according toclaim 4, a first adherend, and a second adherend, wherein the secondadherend is adhered to the electrical debonding type adhesive sheet bythe second adhesive layer, some of the electrical debonding typeadhesive sheet is folded back along an end of the second adherend sothat some of the second adherend is sandwiched, at least some of theprotrudent part is adhered, by the second adhesive layer, to thatsurface of the second adherend which is on the reverse side from thefirst adherend, and the first adherend is adhered to the electricaldebonding type adhesive sheet by a portion of the first adhesive layerwhich is not folded back.
 6. A method for joining and separatingadherends, the method comprising: folding back some of the electricaldebonding type adhesive sheet according to claim 4 along an end of asecond adherend so that some of the second adherend is sandwiched, andadhering the electrical debonding type adhesive sheet to the secondadherend by the second adhesive layer; applying a portion of the firstadhesive layer which is not folded back to a first adherend to join thefirst adherend and the second adherend to each other so that at leastsome of the protrudent part is adhered, by the second adhesive layer, tothat surface of the second adherend which is on the reverse side fromthe first adherend; and thereafter applying a voltage to the firstadhesive layer so as to result in a difference in potential in athickness direction thereof, thereby separating the first adherend andthe second adherend from each other.